Photometric or radiometric calibration involves quantification of light levels (e.g., visible electromagnetic energy (photometric) or emitted energy at any and all wavelengths (radiometric)) required to output a digital pixel value. Such calibration is typically performed using a manual process in which a sequence of photographs of a static scene is taken by a camera set at different exposures, or shutter times. Changes in exposure values provide known luminance ratios between corresponding pixels in the resulting images. A polynomial model fits the resulting data based on, for example, an expected curve or a least squares fitting to obtain the camera's photometric or radiometric response curve (e.g., a photometric response). Such calibration methods rely on assumptions regarding the camera to find a best fit curve; are limited by finite restrictions of shutter control of the camera, modest numbers of light measurement (e.g., typically only few hundred), and curve smoothness assumptions; and often require specialized laboratory equipment.
The following detailed description of certain embodiments of the present invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, certain embodiments are shown in the drawings. It should be understood, however, that the present invention is not limited to the arrangements and instrumentality shown in the attached drawings.